1. Field of the Invention
The present invention relates to a polybutylene terephthalate resin and compositions and molded articles comprising the resin. More particularly, the present invention relates to a polybutylene terephthalate resin which can be molded in a short molding cycle with excellent productivity, exhibits excellent stability to hydrolysis, causes no corrosion of electric contacts and can be advantageously used for members of electric and electronic products such as relays. The present invention further relates to polybutylene terephthalate resin compositions and molded articles which are obtained by adding reinforcing agents and additives to the above resin and exhibit improved impact resistance, stability under heating and oxidation and mold-releasing property.
2. Description of Related Art
Polybutylene terephthalate resins which are typical engineering plastic resins among thermoplastic polyester resins are widely used in the fields of members in automobiles, electric and electronic products and precision instruments since the polybutylene terephthalate resins can be easily molded and exhibit excellent physical and chemical properties such as mechanical properties, heat resistance and electric properties.
Although polybutylene terephthalate resins have the above advantageous properties, it is also known that these resins have some drawbacks. Since polybutylene terephthalate resins absorb little moisture, these resins are essentially not susceptible to the effect of water. However, the ester bond is hydrolyzed with water and water vapor at high temperatures and hydroxyl group and carboxyl group are formed. The formed carboxyl group works as the self-catalyst and further accelerates the hydrolysis. Therefore, in a hot and humid environment, the use of polybutylene terephthalate is restricted. Polybutylene terephthalate resins has carboxyl group derived from terephthalic acid used as the raw material at chain ends thereof. The carboxyl end group also affects the resistance to hydrolysis of polybutylene terephthalate resins.
When a polybutylene terephthalate resin is used for members of electric and electronic products such as relays, there is the possibility that corrosion of metal contacts and attachment of carbonated products at metal contacts take place due to organic gases generated from the resin and the contacts do not work properly. Organic gases generated from the resin also occasionally causes corrosion of molds due to the direct reaction with the molds at high temperatures during molding. It is considered that the organic gases generated from the resin comprise tetrahydrofuran residual in the polybutylene terephthalate resin as the main component although organic gases formed by heat decomposition of the polybutylene terephthalate resin and additives during or after the molding may also be present in minor amounts.
Polybutylene terephthalate resins are resins exhibiting an excellent molding property among engineering resins since the rate of crystallization is relatively great and the molding cycle is short. However, a further improvement in the molding property is desired. It is effective for improving the molding property that the crystallization temperature of the polybutylene terephthalate is elevated.
To reduce the amount of carboxyl end group, a lower reaction temperature and a shorter reaction time can be adopted in the production of the polybutylene terephthalate. However, the molecular weight of the obtained polybutylene terephthalate resin becomes smaller under these conditions. To overcome this drawback, a process in which a polybutylene terephthalate resin produced by the polymerization in the melted condition at a relatively low temperature for a relatively short time is further treated by the solid phase polymerization to increase the molecular weight, is known.
For example, in Japanese Patent Application Laid-Open No. Heisei 7(1995)-149880, an invention on a novel polybutylene terephthalate resin which has less than 30 meq/kg of COOH end group and a number-average molecular weight (Mn) of at least 30,000 and exhibits an excellent bonding property to lacquers is disclosed. In the examples of this invention, it is shown that PBT-4 having 7.5 meq/kg of COOH group at the chain ends and Mn of 41,200 could be obtained when dimethyl terephthalate and butanediol were treated by polycondensation, followed by post condensation in the solid phase.
In Japanese Patent Application Laid-Open No. Heisei 6(1994)-256628, it is proposed that a polybutylene terephthalate resin having 20 eq/106 g or less of carboxyl end group is used for improving resistance to hydrolysis of a polybutylene terephthalate resin composition comprising flame retardants. As the process for obtaining the polybutylene terephthalate resin having carboxyl end group in such a small amount, a process in which, in polycondensation of 1,4-butanediol and terephthalic acid or an ester thereof with a lower alcohol, the polycondensation is stopped in the melted condition when the intrinsic viscosity reaches 0.1 to 0.55 dl/g and, after solidifying the product by cooling, solid phase polycondensation is conducted to achieve an intrinsic viscosity of 0.6 to 2 dl/g, is disclosed.
In the specifications of the above applications, no descriptions on the content of tetrahydrofuran or the crystallization temperature can be found. Although the polybutylene terephthalate resins described above have decreased amounts of carboxyl end group, the content of tetrahydrofuran and the crystallization temperature are not known.
In Japanese Patent Application Laid-Open No. 2000-111768, an invention on a loose tube for optical fibers comprising a polybutylene terephthalate resin which contains 0.30% by weight or smaller of butylene terephthalate oligomer, generates 10 ppm or less of volatile gases by a heat treatment at 150xc2x0 C. for 60 minutes and has a concentration of carboxyl end group of 30 eq/t or smaller and an inherent viscosity of 1.0 to 1.2 dl/g is described. In the above application, it is described that excellent resistance to hydrolysis is exhibited and formation of gum is suppressed in extrusion when the above resin is used. However, no descriptions can be found on the crystallization temperature of the polybutylene terephthalate resin. In the above application, the method for decreasing the concentration of oligomers of the polybutylene terephthalate resin is shown. However, the processes for decreasing the amounts of volatile gases and carboxyl end group to the desired values are not disclosed. No descriptions can be found on the process for preparing the polybutylene terephthalate resin used in the above application, either.
To prevent occurrence of poor contact due to organic gases generated from molded articles such as relays and switches using a polybutylene terephthalate resin, it has heretofore been known that the molded articles are degassed by baking in a vacuum. However, the baking in a vacuum has drawbacks in that productivity is small and that the treated molded articles lose gloss or become fragile due to loss of toughness.
In Japanese Patent Application Laid-Open No. Heisei 8(1996)-209004, a thermoplastic resin composition for members of electric and electronic products having contacts in which 0.2 to 10 parts by weight of a polyol such as 1,4-butanediol and polyethylene glycol is added to 100 parts by weight of a thermoplastic resin such as a polybutylene terephthalate resin is proposed as the material for solving the above problems on the degassing by baking in a vacuum. It is described in this application that, when the resin composition is heated, a gas generated from the aliphatic polyol works on electric contacts as a protective component on the contacts and suppresses an increase in resistance of contact and the occurrence of poor contact can be prevented. However, fouling of molds and decreases in mechanical properties of molded articles of the resin are inevitable when the polyol is added in such a great amount.
In Japanese Patent Application Laid-Open No. Heisei 8(1996)-227030, an invention on a covering tube for optical fibers obtained by extrusion of a polybutylene terephthalate resin or a composition thereof is described. It is described in this application that the polybutylene terephthalate resin preferably satisfies the following condition: Tmxe2x88x92Ticxe2x89xa630, wherein Tm represents the melting point of the resin and Tic represents an extrapolated starting temperature of crystallization of the resin. To satisfy this condition, it is necessary that the crystallization temperature of the resin be elevated. However, a method of adding a nucleating agent of crystallization such as boron nitride is used as the means for elevating the crystallization temperature of the polybutylene terephthalate resin and no descriptions can be found on the elevation of the crystallization temperature of the resin itself. Moreover the concentrations of carboxyl end group in the polybutylene terephthalate resins described in the above application is 40 meq/kg or greater in all cases.
As described above, polybutylene terephthalate resins in which one or two factors among the amount of carboxyl end group, the amount of residual tetrahydrofuran and the crystallization temperature are controlled have been known. However, no polybutylene terephthalate resins in which all three factors are controlled have been known as far as the present inventors are aware of.
The present invention has an object of providing a polybutylene terephthalate resin which can be molded in a short molding cycle with excellent productivity, exhibits excellent stability to hydrolysis, causes no corrosion of electric contacts and can be advantageously used for members of electric and electronic products such as relays, polybutylene terephthalate resin compositions which are obtained by adding reinforcing agents and/or additives to the above resin and exhibit further improved impact resistance, stability under heating and oxidation and mold-releasing property and a molded article comprising the resin or the composition.
As the result of intensive studies to overcome the above drawbacks, it was found that a polybutylene terephthalate resin having 30 eq/t or less of carboxyl end group, a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher and an amount of residual tetrahydrofuran of 300 ppm by weight or less could be molded in a short molding cycle with excellent productivity, exhibited excellent stability to hydrolysis and caused no corrosion of metals and that polybutylene terephthalate resin compositions and molded articles exhibiting further improved impact resistance, stability under heating and oxidation and molding property could be obtained by adding glass fiber, antioxidants and mold-releasing agents to the above polybutylene terephthalate resin. The present invention has been completed based on this knowledge.
The present invention provides:
(1) A polybutylene terephthalate resin having 30 eq/t or less of carboxyl end group and a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min;
(2) A resin described in (1), which has an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin;
(3) A resin described in (1), which has an amount of residual tetrahydrofuran of 50 to 300 ppm by weight or less in the polybutylene terephthalate resin;
(4) A resin described in (1), which has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,3,2-tetrachloroethane in relative amounts by weight of 1/1;
(5) A resin described in (1), which is obtained by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(6) A polybutylene terephthalate resin which has a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min and an amount of residual tetrahydrofuran of 300 ppm by weight or less in the resin;
(7) A resin described in (6), which has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(8) A resin described in (6), which is prepared by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(9) A polybutylene terephthalate resin composition which comprises a polybutylene terephthalate resin which has 30 eq/t or less of carboxyl end group and a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min, and glass fiber;
(10) A composition described in (9), wherein the polybutylene terephthalate resin has an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin;
(11) A composition described in (9), wherein the polybutylene terephthalate resin has an amount of residual tetrahydrofuran of 50 to 300 ppm.
(12) A composition described in (9), wherein the polybutylene terephthalate resin has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(13) A composition described in (9), wherein the polybutylene terephthalate resin is obtained by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(14) A composition described in (9), which comprises glass fiber in an amount of 3 to 150 parts by weight per 100 parts by weight of the polybutylene terephthalate resin;
(15) A polybutylene terephthalate resin composition which comprises a polybutylene terephthalate resin which has a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min and an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin, and glass fiber;
(16) A composition described in (15), wherein the polybutylene terephthalate resin has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(17) A composition described in (15), wherein the polybutylene terephthalate resin is a resin produced by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(18) A polybutylene terephthalate resin composition which comprises a polybutylene terephthalate resin which has 30 eq/t or less of carboxyl end group and a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min, and phenolic antioxidants;
(19) A composition described in (18), which further comprises at least one antioxidant selected from a group consisting of sulfur-based antioxidants and phosphorus-based antioxidants;
(20) A composition described in (18), wherein the phenolic antioxidants are hindered phenolic antioxidants;
(21) A composition described in (19), wherein the sulfur-based antioxidants are thioether-based antioxidants;
(22) A composition described in 18, which has an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin;
(23) A composition described in (18), wherein the polybutylene terephthalate resin has an amount of residual tetrahydrofuran of 50 to 300 ppm.
(24) A composition described in (18), wherein the polybutylene terephthalate resin has an inherent intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(25) A composition described in (18), wherein the polybutylene terephthalate resin is a resin produced by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(26) A composition described in (18), which comprises the phenolic antioxidants in an amount of 0.001 to 2 parts by weight per 100 parts by weight of the polybutylene terephthalate resin;
(27) A polybutylene terephthalate resin composition which comprises a polybutylene terephthalate resin which has a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min and an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin, and phenolic antioxidants;
(28) A composition described in (27), which further comprises at least one antioxidant selected from a group consisting of sulfur-based antioxidants and phosphorus-based antioxidants;
(29) A composition described in (27), wherein the phenolic antioxidants are hindered phenolic antioxidants;
(30) A composition described in (28), wherein the sulfur-based antioxidants are thioether-based antioxidants;
(31) A composition described in (27), wherein the polybutylene terephthalate resin has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(32) A composition described in (27), wherein the polybutylene terephthalate resin is a resin produced by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(33) A polybutylene terephthalate resin composition which comprises a polybutylene terephthalate resin which has 30 eq/t or less of carboxyl end group and a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min, and a fatty acid ester which has a residue group of a fatty acid having 12 to 36 carbon atoms and a residue group of an alcohol having 1 to 36 carbon atoms;
(34) A composition described in (33), which has an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin;
(35) A composition described in (33), wherein the polybutylene terephthalate resin has an amount of residual tetrahydrofuran of 50 to 300 ppm.
(36) A composition described in (33), wherein the polybutylene terephthalate resin has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(37) A composition described in (33), wherein the polybutylene terephthalate resin is a resin produced by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials;
(38) A composition described in (31), which comprises the fatty acid ester in an amount of 0.01 to 2 parts by weight per 100 parts by weight of the polybutylene terephthalate resin;
(39) A polybutylene terephthalate resin composition which comprises a polybutylene terephthalate resin which has a crystallization temperature in a temperature decrease of 175xc2x0 C. or higher as measured by a differential scanning calorimeter at a rate of the temperature decrease of 20xc2x0 C./min and an amount of residual tetrahydrofuran of 300 ppm by weight or less in the polybutylene terephthalate resin, and a fatty acid ester which has a residue group of a fatty acid having 12 to 36 carbon atoms and a residue group of an alcohol having 1 to 36 carbon atoms;
(40) A composition described in (39), wherein the polybutylene terephthalate resin has an intrinsic viscosity of 0.5 to 1.5 dl/g as measured at 30xc2x0 C. in a mixed solvent composed of phenol and 1,1,2,2-tetrachloroethane in relative amounts by weight of 1/1;
(41) A composition described in (39), wherein the polybutylene terephthalate resin is a resin produced by continuous polycondensation using terephthalic acid and 1,4-butanediol as main raw materials; and
(42) A molded article obtained by molding the polybutylene terephthalate resin described in (1).